[3/3] media: ov5640: Honor power on time in init_setting

From: Nishanth Menon <nm@ti.com>

OV5640 Datasheet[1] Figures 2-3 and 2-4 indicate the timing sequences
that is expected during various initialization steps. Note the power
on time includes t0 + t1 + t2 >= 5ms, delay for poweron.

As indicated in section 2.8, the PWDN assertion can either be via
external pin control OR via the register 0x3008 bit 6 (see table 7-1 in
[1])

[1] https://cdn.sparkfun.com/datasheets/Sensors/LightImaging/OV5640_datasheet.pdf

Fixes: 19a81c1426c1 ("[media] add Omnivision OV5640 sensor driver")
Signed-off-by: Nishanth Menon <nm@ti.com>
---
 drivers/media/i2c/ov5640.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

Hi Jai

On Fri, Dec 16, 2022 at 07:14:09PM +0530, Jai Luthra wrote:
> From: Nishanth Menon <nm@ti.com>
>
> OV5640 Datasheet[1] Figures 2-3 and 2-4 indicate the timing sequences
> that is expected during various initialization steps. Note the power
> on time includes t0 + t1 + t2 >= 5ms, delay for poweron.
>
> As indicated in section 2.8, the PWDN assertion can either be via
> external pin control OR via the register 0x3008 bit 6 (see table 7-1 in
> [1])
>
> [1] https://cdn.sparkfun.com/datasheets/Sensors/LightImaging/OV5640_datasheet.pdf
>
> Fixes: 19a81c1426c1 ("[media] add Omnivision OV5640 sensor driver")
> Signed-off-by: Nishanth Menon <nm@ti.com>
> ---
>  drivers/media/i2c/ov5640.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/media/i2c/ov5640.c b/drivers/media/i2c/ov5640.c
> index fa84e60de0db..ff2a2c9358e7 100644
> --- a/drivers/media/i2c/ov5640.c
> +++ b/drivers/media/i2c/ov5640.c
> @@ -608,7 +608,7 @@ static const struct reg_value ov5640_init_setting[] = {
>  	{0x583b, 0x28, 0, 0}, {0x583c, 0x42, 0, 0}, {0x583d, 0xce, 0, 0},
>  	{0x5025, 0x00, 0, 0}, {0x3a0f, 0x30, 0, 0}, {0x3a10, 0x28, 0, 0},
>  	{0x3a1b, 0x30, 0, 0}, {0x3a1e, 0x26, 0, 0}, {0x3a11, 0x60, 0, 0},
> -	{0x3a1f, 0x14, 0, 0}, {0x3008, 0x02, 0, 0}, {0x3c00, 0x04, 0, 300},
> +	{0x3a1f, 0x14, 0, 0}, {0x3008, 0x02, 0, 5}, {0x3c00, 0x04, 0, 300},

Two observations:

as per the description of register 0x3008

3008 default value = 0x02
3008[7] = Software Reset
3008[6] = Software Power Down

The init_settings[] register table has these entries at the very
beginning

	{0x3008, 0x82, 0, 5}, {0x3008, 0x42, 0, 0},

and ends with the entry you have modified

        {0x3008, 0x02, 0, 5}

As I read from the 2.8 section of the datasheet

A reset can also be initiated through the SCCB interface by setting
register 0x3008[7] to high.

So I presume the first two registers entries:

	{0x3008, 0x82, 0, 5} -> Start a SW reset and wait 5 msec
                                for the chip to resume
	{0x3008, 0x42, 0, 0} -> SW standby mode

SW standby mode is described as:

        Executing a software standby through the SCCB interface
        suspends internal circuit activity but does not halt the
        device clock. All register content is maintained in standby
        mode.

I presume that the first

	{0x3008, 0x42, 0, 0}

 exists from SW standby mode to program the chip and the last

        {0x3008, 0x02, 0, 5}

puts the chip in sw standby at the end of init_settings[].
Software standby is then exited by ov5640_set_stream_dvp() for DVP and
by clearing 0x300e[4:3] in MIPI mode, as the datasheet reports:

        To initiate hardware standby mode, the PWDN pin must be tied to high
        (while in MIPI mode, set register 0x300E[4:3] to 2’b11 before the PWDN
        pin is set to high)

My second observation is that those entries in the init_settings[]
table performs SW reset/standby regardless if there's a GPIO or not
installed to control the reset and pwdn lines.

Would it be worth in your opinion trying to modify ov5640_power()
and ov5640_reset() to use either SW or HW standby/reset conditionally
on the avialability of sensor->reset_gpio and sensor->pwdn_gpio and
remove the initial SW standby/reset from init_setting[] ?

>  };
>
>  static const struct reg_value ov5640_setting_low_res[] = {
> --
> 2.17.1
>

Hi Jai

On Mon, Dec 19, 2022 at 06:38:54PM +0530, Jai Luthra wrote:
> Hi Jacopo,
>
> Thank you for the comments.
>
> On 19/12/22 15:40, Jacopo Mondi wrote:
> > Hi Jai
> >
> > On Fri, Dec 16, 2022 at 07:14:09PM +0530, Jai Luthra wrote:
> > > From: Nishanth Menon <nm@ti.com>
> > >
> > > OV5640 Datasheet[1] Figures 2-3 and 2-4 indicate the timing sequences
> > > that is expected during various initialization steps. Note the power
> > > on time includes t0 + t1 + t2 >= 5ms, delay for poweron.
> > >
> > > As indicated in section 2.8, the PWDN assertion can either be via
> > > external pin control OR via the register 0x3008 bit 6 (see table 7-1 in
> > > [1])
> > >
> > > [1] https://cdn.sparkfun.com/datasheets/Sensors/LightImaging/OV5640_datasheet.pdf
> > >
> > > Fixes: 19a81c1426c1 ("[media] add Omnivision OV5640 sensor driver")
> > > Signed-off-by: Nishanth Menon <nm@ti.com>
> > > ---
> > >   drivers/media/i2c/ov5640.c | 2 +-
> > >   1 file changed, 1 insertion(+), 1 deletion(-)
> > >
> > > diff --git a/drivers/media/i2c/ov5640.c b/drivers/media/i2c/ov5640.c
> > > index fa84e60de0db..ff2a2c9358e7 100644
> > > --- a/drivers/media/i2c/ov5640.c
> > > +++ b/drivers/media/i2c/ov5640.c
> > > @@ -608,7 +608,7 @@ static const struct reg_value ov5640_init_setting[] = {
> > >   	{0x583b, 0x28, 0, 0}, {0x583c, 0x42, 0, 0}, {0x583d, 0xce, 0, 0},
> > >   	{0x5025, 0x00, 0, 0}, {0x3a0f, 0x30, 0, 0}, {0x3a10, 0x28, 0, 0},
> > >   	{0x3a1b, 0x30, 0, 0}, {0x3a1e, 0x26, 0, 0}, {0x3a11, 0x60, 0, 0},
> > > -	{0x3a1f, 0x14, 0, 0}, {0x3008, 0x02, 0, 0}, {0x3c00, 0x04, 0, 300},
> > > +	{0x3a1f, 0x14, 0, 0}, {0x3008, 0x02, 0, 5}, {0x3c00, 0x04, 0, 300},
> >
> > Two observations:
> >
> > as per the description of register 0x3008
> >
> > 3008 default value = 0x02
> > 3008[7] = Software Reset
> > 3008[6] = Software Power Down
> >
> > The init_settings[] register table has these entries at the very
> > beginning
> >
> > 	{0x3008, 0x82, 0, 5}, {0x3008, 0x42, 0, 0},
> >
> > and ends with the entry you have modified
> >
> >          {0x3008, 0x02, 0, 5}
> >
> > As I read from the 2.8 section of the datasheet
> >
> > A reset can also be initiated through the SCCB interface by setting
> > register 0x3008[7] to high.
> >
> > So I presume the first two registers entries:
> >
> > 	{0x3008, 0x82, 0, 5} -> Start a SW reset and wait 5 msec
> >                                  for the chip to resume
> > 	{0x3008, 0x42, 0, 0} -> SW standby mode
> >
> > SW standby mode is described as:
> >
> >          Executing a software standby through the SCCB interface
> >          suspends internal circuit activity but does not halt the
> >          device clock. All register content is maintained in standby
> >          mode.
>
> I agree with everything above.
>
> >
> > I presume that the first
> >
> > 	{0x3008, 0x42, 0, 0}
> >
> >   exists from SW standby mode to program the chip and the last
>
> Here I'm a little confused. Isn't it the opposite according to the
> datasheet?
>
> Setting the register to 0x42 (bit 6 = 1) initiates SW standby, which I
> assume stops all other functions on the chip but still allows programming
> registers.
>

I haven't found any mention about the BIT(6) polarity. IOW I haven't
found documented if setting it to 1 enters or exists SW standby mode.

Your reasoning is valid, I'm just a bit surprised the SCCB is active
and registers can be programmed while in standby mode.

However, this

#define OV5640_REG_SYS_CTRL0_SW_PWDN	0x42
#define OV5640_REG_SYS_CTRL0_SW_PWUP	0x02

seems to confirm what you said.

> >
> >          {0x3008, 0x02, 0, 5}
> >
> > puts the chip in sw standby at the end of init_settings[]
>
> Then setting 0x02 (bit 6 = 0) exits from SW standby in case of MIPI.
>
> For DVP though, I see that we skip setting 0x02 to that register in
> ov5640_load_regs(), so sensor stays in SW standby mode until
> ov5640_set_stream_dvp() is called.
>

That's what confused me. init_settings[] are programmed for both DVP
and MIPI. If the last write to 0x3008 is 0x02 there shouldn't be any
need to re-program it. However since ov5640_set_stream_dvp() is called
in the s_stream() call path it means SW standby is entered between
every streaming session.

Please note that no 5msec delay is respected when
existing/entering sw standby between streaming session.


> > Software standby is then exited by ov5640_set_stream_dvp() for DVP and
> > by clearing 0x300e[4:3] in MIPI mode, as the datasheet reports:
> >
> >          To initiate hardware standby mode, the PWDN pin must be tied to high
> >          (while in MIPI mode, set register 0x300E[4:3] to 2’b11 before the PWDN
> >          pin is set to high >
> > My second observation is that those entries in the init_settings[]
> > table performs SW reset/standby regardless if there's a GPIO or not
> > installed to control the reset and pwdn lines.
> >
> > Would it be worth in your opinion trying to modify ov5640_power()
> > and ov5640_reset() to use either SW or HW standby/reset conditionally
> > on the avialability of sensor->reset_gpio and sensor->pwdn_gpio and
> > remove the initial SW standby/reset from init_setting[] ?
>
> I don't think we can use the SCCB register pwdn & reset for the initial
> sensor power up sequence, as sensor SCCB depends on the correct sequence
> being followed on hardware pins. From Section 2.8:

I was suggesting to use sw reset/powerup if no gpios are registered.

>
> 	Manually applying a hard reset upon power up is required even
> 	though on-chip reset is included.
>

Do you interpret "Manually applying a reset upon power up" to imply
"software reset" ? As I read it it doesn't require the reset to be
SW or HW.

> But I agree, if some module does not wire the pins at all then we might have
> to ignore the datasheet here and try it using the register.
>

That's what I was suggesting. If you have gpios you shouldn't need
initial SW resets and powerup. If you don't have gpios, use sw reset
so that the reset/powerup routines are centralized and not spread between
register tables and functions ?

What setup are you testing with ? DVP or MIPI ? With gpios or without
? I can test on a 2-data lanes MIPI setup with HW gpio lines if it
helps.

Thanks
  j



> >
> > >   };
> > >
> > >   static const struct reg_value ov5640_setting_low_res[] = {
> > > --
> > > 2.17.1
> > >
>
> Thanks,
> Jai